LPS vs SPS vs Soft Corals: Which Type Belongs in Your Reef?

Walk into any reef keeping forum and you'll encounter three acronyms constantly: softies, LPS, and SPS. These are not just labels — they describe three fundamentally different categories of coral with different biology, different requirements, and different tolerances for the mistakes that every reef keeper inevitably makes.

Understanding the difference is not just academic. Putting an SPS coral in a tank built for softies, or misidentifying an LPS as something hardier than it is, leads to bleached and dying coral. This guide breaks down each category and where it fits on the difficulty ladder.

The role of zooxanthellae in all three types

Before diving into categories, it helps to understand what all photosynthetic coral has in common. Most reef corals host symbiotic dinoflagellate algae called zooxanthellae inside their tissue. These microscopic algae photosynthesize — converting light into sugars — and pass a significant portion of that energy to their coral host. In return, the coral provides the algae with shelter and nutrients.

When water temperatures spike, or certain parameters go wrong, coral expels its zooxanthellae. The coral turns white — this is bleaching — and without its photosynthetic partner, it can starve within weeks. Everything about lighting, temperature management, and flow in a reef tank ultimately serves to keep zooxanthellae healthy and in place.

Soft corals (softies)

Soft corals have no calcium carbonate skeleton. Their structure is supported by a protein-based matrix reinforced with tiny calcium carbonate spicules, but they do not calcify the way stony corals do. This means they are far less demanding of alkalinity and calcium levels, and far more tolerant of parameter fluctuations.

Common soft coral species

• Mushroom corals (Discosoma, Rhodactis, Actinodiscus): Single large polyps that spread across rock. Extremely tolerant of low light and low flow. The stereotypical "first coral." Many experienced hobbyists still keep them because colorful morphs are genuinely beautiful.
• Zoanthids (Zoanthus, Palythoa): Colonial polyps that form mats of tightly packed buttons. Fast-growing and available in hundreds of color morphs. Easy to keep, but contain palytoxin — wear gloves and eye protection when handling or fragging.
• Leather corals (Sarcophyton, Sinularia, Lobophytum): Large, fast-growing corals that periodically close completely and shed a waxy film — this is normal and alarming the first time you see it. They do not sting neighbors, but they do release terpenes that can irritate nearby coral.
• Xenia: Pulsing, rhythmic soft corals that are either loved or despised. They grow aggressively — treat them as potentially invasive — but are nearly impossible to kill accidentally.
• Kenya tree (Capnella): Branching soft coral that tolerates low flow and moderate light. Drops branches frequently as a natural propagation mechanism; these babies will colonize wherever they land.

Soft corals thrive in moderate flow and light, and tolerate a wide range of parameters. They are the appropriate starting point for any new tank and any new reef keeper.

LPS corals (Large Polyp Stony)

LPS corals have a calcium carbonate skeleton and large, fleshy polyps that extend significantly beyond the skeletal structure. They calcify and consume alkalinity and calcium, but more slowly than SPS. They represent the intermediate tier — more demanding than softies, far more forgiving than SPS — and are where most serious hobbyists spend the majority of their time and money.

Common LPS species

• Hammer coral (Euphyllia ancora): Named for its hammer-shaped polyp tips. Available in gold, green, and ultra-grade purple morphs. One of the most popular corals in the hobby. Needs stable alkalinity and moderate-to-high flow.
• Torch coral (Euphyllia glabrescens): Similar to hammer but with tentacle-tipped polyps that flow in current. Sensitive to flow — too much collapses the polyps; too little and they never fully extend. Also susceptible to "brown jelly disease" if stressed.
• Frogspawn (Euphyllia divisa): Branching Euphyllia with grape-like polyp clusters. The Euphyllia genus as a whole is somewhat allelopathic — give them space from unrelated coral.
• Candy cane coral (Caulastrea furcata): A beginner-friendly LPS with small, neatly organized circular polyps. Very tolerant of parameter variation compared to most LPS.
• Brain corals (Favites, Lobophyllia, Trachyphyllia): Heavy, dome-shaped corals with maze-like surface patterns. Lobophyllia in particular is a good feeder — it accepts meaty foods directly. Favites can be aggressive sweepers; give them room.
• Elegance coral (Catalaphyllia jardinei): Beautiful, deceptively tricky LPS. Has specific placement requirements (typically in sand, not on rock) and is sensitive to handling. Often listed as beginner-unfriendly despite its appearance.

LPS need stable alkalinity (8–11 dKH), stable calcium (400–450 ppm), moderate to high flow, and medium to high light (100–250 PAR). Most tolerate the occasional parameter swing that would RTN an SPS coral. Tank maturity of 3–6 months before adding sensitive LPS is a good rule.

SPS corals (Small Polyp Stony)

SPS corals are the pinnacle of reef keeping difficulty. They are fast calcifiers with tiny polyps that live in close proximity across a dense colony surface. Because they build skeleton rapidly, they consume alkalinity and calcium at rates that can noticeably change your water chemistry daily in a well-grown tank. They require pristine water, high flow, and high PAR.

Common SPS species

• Acropora: The crown jewel of SPS and the most demanding coral commonly kept. Branching, table, and bottlebrush growth forms. Sensitive to alkalinity swings, low flow, high nutrients, and inadequate light. A well-kept acropora colony growing under good lighting is one of the most spectacular things in the hobby.
• Montipora: The gateway SPS. Encrusting and plating growth forms are more forgiving than branching acropora. Many hobbyists start SPS with Montipora capricornis (the "cap") before moving to acropora.
• Stylophora and Pocillopora: Branching SPS that are more forgiving than acropora but more demanding than montipora. Good intermediate SPS to build experience with.
• Seriatopora (birdsnest): Fast-growing branching SPS with thin, delicate branches. Indicator coral — it often shows stress (browning, STN from the tips) before tougher corals do. Treat it as an early warning system.

SPS require low nitrate (under 10 ppm), low phosphate (under 0.1 ppm), highly stable alkalinity, high flow (multiple wavemakers), and high PAR (200–400+). Do not attempt SPS in a tank under 6 months old, and do not rush.

The difficulty ladder

As a rough guide to progression through the hobby:

Mushroom corals → Zoanthids → Leather corals → Candy cane (Caulastrea) → Hammer coral → Torch coral → Brain corals → Montipora → Stylophora / Pocillopora → Acropora

This is not absolute — individual coral health, tank conditions, and source quality all matter — but it maps reasonably well to what consistently survives in imperfect conditions versus what requires near perfection.